This invention relates to a caliper brake for a bicycle, whose brake shoes are pressed against side faces of a rim of one wheel of the bicycle to brake it.
In general, there are three kinds of caliper brakes, center-pull, side-pull and cantilever types. The brake of the invention belongs to the side-pull type caliper brake.
Before explaining conventional brakes, frame members of a bicycle are explained referring to FIGS. 1-3a and 3b. A bicycle as shown comprises a head tube 1, fork blades 2, a top tube 3, a front or down tube 4, a seat tube 5, chain stays 6 and seat stays 7. Another bicycle shown in FIG. 2b comprises a main frame 8. The bicycle further comprises a band brake 9, a rear wheel 10 having a wheel 10a and a rim 10b, a bottom bracket 11, chain wheel cranks 12 and a chain wheel 13.
FIGS. 2a and 2b illustrate a diamond-shaped frame and a U-shaped frame for bicycles, respectively, and FIGS. 2c and 2d illustrate staggered frames and FIGS. 2e and 2f illustrate roop-shaped frames.
In the case of the diamond-shaped frame of a bicycle shown in FIG. 2a, an operating wire 14 connected to brake levers (not shown) provided at handlebars can be extended easily rearwardly along the front tube 4 as shown in a solid line or along the top tube 3 as shown in two dot-and-dash line without any trouble.
With the bicycles shown in FIGS. 2b-2f other than the diamond-shaped frame bicycle, however, the operating wires 14 must contain many sharply bent portions in order to extend the wire 14 from the handlebars to the seat stays 7. As a result, frictional resistance in the brake wire consisting of an inner and an outer wire disadvantageously increases.
In order to avoid such bent portions of the brake wire in the bicycles shown in FIGS. 2b-2f, the brake may be provided on the chain stays 6 as shown in FIG. 1.
FIG. 1 illustrates a brake including side-pull type caliper arms 15A and 15B of the prior art mounted on chain stays 6. With this arrangement, however, free ends 15Aa and 15Ba of the caliper arms 15A and 15B would interfere with the chain wheel cranks 12, respectively. Therefore, it is impossible to mount the brake on the chain stays 6.
In the drawing, reference numeral 16 denotes a connecting plate spanned or bridged on undersides of the chain stays 6 and fixed thereat. The caliper arms 15A and 15B are pivotally rotatably supported on the connecting plate 16 by means of a bolt 17. A brake wire consists of an outer wire 18 having at its end an adjusting screw 18a fixed to a free end 15Ba of the caliper arm 15B and an inner or operating wire 19 having an end 19a fixed to the free end 15Aa of the caliper arm 15A. Brake shoes 20 are fixed to the other ends of the caliper arms 15A and 15B in opposition to a rim 10b of a wheel.
In the case that the free ends 15Aa and 15Ba of the caliper arm 15A and 15B interfere with other components of the bicycle, such an interference may be eliminated by limiting the outward extensions of the caliper arms. However, since the rotating radii of the caliper arms become smaller, a force acting upon the operating wire 19 must be increased in order to obtain a pressing force of the brake shoes 20 against the rim 10b substantially equal to that of the case having the previous longer rotating radii.
However, operating wires for bicycles are generally used at uppermost limits allowed by their mechanical properties. If the operating wires 19 are subjected to larger forces in use, they would exhibit excessive elongations and the larger forces detrimentally affect their strength and durability.
It has been proposed to use a running pulley block having two pulleys rotatably connected by two side plates for a center-pull type brake of a bicycle as disclosed in Japanese Utility Model Application Publication No. 52-3,799. In more detail, an operating wire having one end fixed to a frame of the bicycle extends about one of the pulleys and the other end is pulled when a brake action is applied to the brake. On the other hand, ends of caliper brake arms are connected by a connecting wire whose center extends about the other pulleys.
With this arrangement, since the running pulley block is moved a distance one half of a moved distance of the operating wire pulled by an operation of brake levers at handlebars, the force caused by the connecting wire connecting the caliper brake arms is advantageously twice the force on the operating wire caused by the brake levers. However, since strokes of brake shoes become one half of original strokes in case directly pulling the connecting wire without using the running pulley block, clearances between the brake shoes and a rim of a wheel of the bicycle must be one half of original clearances. Therefore, the brake shoes are likely to contact the rim of the wheel and require frequent adjustment of clearances particularly in the event that the connecting wire connecting the caliper brake arms has been elongated and movable portions have been worn.
Moreover, outwardly extending portions of the brake interfere with feet and clothes of a cyclist and the brake itself is likely to be damaged when the bicycle falls down.